Method for Controlling Delivery Quantity, and Reciprocating Compressor Having Delivery Quantity Control

ABSTRACT

The invention relates to a method for delivery quantity control of a reciprocating compressor, wherein the motion of a closing organ ( 5   b ) of an automatic suction valve ( 5 ) is influenced during at least one part of a cycle of the crankshaft by means of a refraction gripper ( 6 ), wherein the method comprises a continuously variable return flow control, wherein the retraction gripper ( 6 ) contacts the closing organ ( 5 b) and prevents the same from closing during a first partial segment (K 1 ) of the cycle of the crankshaft, and wherein the retraction gripper ( 6 ) is retracted during a second partial segment (K 2 ) of the cycle of the crankshaft and the closing organ ( 5   b ) is closed, wherein the retraction gripper ( 6 ) is retracted such that the speed of the moving closing organ ( 5   b ) is reduced prior to contacting the suction valve ( 5 ).

The invention concerns a method for controlling delivery quantity of areciprocating compressor according to the preamble of claim 1. Theinvention further concerns a reciprocating compressor with deliveryquantity control according to the preamble of claim 12.

BACKGROUND ART

Documents EP 0 801 227 A2 and EP 1 400 692 disclose a method forinfluencing the pressure-dependent, self-acting, periodic openingmovement of a closing body of an intake valve of a reciprocatingcompressor by means of a control device which influences the closingbody, as necessary, over at least a part of the crank rotation. Sincethe service life of self-acting compressor valves, as mostly used on theintake and the pressure side, is primarily influenced by theimpact-stress-requirement of the alternating impingement of the actualclosing body on, respectively, the seat or backstop, the above-mentioneddocuments disclose a method in which the intake valve is forcefullyopened before reaching pressure equilibrium by using a so-calledunloader (or ‘lift off gripper’), in order to avoid a sharp,instantaneous acceleration of the closing body towards the backstop,which would occur upon automatic opening. This enables reduction of theimpact-stress-requirement of the compressor valve.

This method has the disadvantage that the compressor valves, as used onthe intake side and, in particular, those used on the pressure side,still have a high stress-requirement, particularly when the compressorsystem is run using continuously variable backflow regulation methods.With continuously variable backflow regulation, the intake valve is heldopen with the help of the unloader during a partial angular range of thecompression cycle and is thereafter shut, in order to thereby influencethe delivery quantity.

A disadvantage of this known method is the fact that the closing body ofthe intake valve and of the pressure valve is subject to relatively highwear, which requires a correspondingly high maintenance effort.

PRESENTATION OF THE INVENTION

The problem to be solved by the invention is to provide a moreadvantageous method for controlling delivery quantity of a reciprocatingcompressor. This problem is solved by a method having the features ofclaim 1. Dependent claims 2 to 11 concern further advantageous methodsteps. The problem is further solved by a reciprocating compressorhaving the features of claim 12. Dependent claims 13 to 17 concernfurther, advantageous embodiments.

In particular, the problem is solved by a method for delivery quantitycontrol of a reciprocating compressor, in which the movement of aclosing body of a self-acting intake valve is influenced during at leastpart of a cycle of crank rotation by an unloader driven by a controldevice, wherein the method comprises a continuously variable backflowregulation, in which the unloader lies against the closing body during afirst section of the cycle of crank rotation and prevents its closure,and in which the unloader is driven back during a second section of thecycle of crank rotation and the closing body is closed, wherein theunloader is driven back in such a way that the speed of the movingclosing body is reduced prior to its seating on the intake valve.

In a further advantageous method, this comprises a skip regulation, inwhich the unloader prevents closure of the closing body during a wholecycle of crank rotation, wherein the delivery quantity is regulated byat least a combination of continuously variable backflow regulation andskip regulation.

In the method according to the invention, the delivery quantity isregulated by the forced holding open of the intake valve. In the courseof doing this, preferably two different regulation methods are used,namely a skip regulation and the continuously variable backflowregulation. Both methods employ a so-called unloader, which presses theclosing body of the valve, for example a plate valve, ring valve orpoppet valve, into an open position and preferably, onto the valve seat.

The reciprocating compressor has a compression space, to which gas isintroduced via an intake valve and from which compressed gas is led awayvia an outlet valve, also called pressure valve. In the skip regulationmethod, the closing body of the intake valve is held open during a wholeworking stroke or a complete work cycle. This causes the pressure in thecompression space to not rise above the pressure required to open thepressure valve during the compression phase, such that the aspirated gasis pressed back into the intake conduit during the compression phase andthus compression and further transport into the pressure conduit are notavailable. The pressure valve thus remains shut and thus thiscompression space does not convey any gas via the pressure valve intothe pressure conduit. If skip regulation is deactivated, i.e. normaloperation executed, then the compression space again conveys the wholegas stream via the pressure valve into the pressure conduit. If thereciprocating compressor has, for example, only one compression space,then skip regulation may be run such that certain working cycles areexecuted normally and skip regulation is activated during certainworking cycles. In this way, a disadvantage of skip regulation is thatthe amount of gas conveyed from the reciprocating compressor can only beregulated in a stepwise manner. A further disadvantage of skipregulation is that there is no flow through the unloaded compressionspace, i.e. with non-opening pressure valve, and thus dirt can collectin the compression space, which raises valve wear or respectively wearof the packing rings and piston rings.

In the backflow regulation method, the intake valve is held open withthe help of the unloader during a partial angular range of a completecompression stroke or respectively of a complete crank rotation andthereafter is shut, in order to thereby influence the delivery quantity.In doing this, the intake valve is only pressed open by the unloader atthe beginning of the compression phase. In this way, a part of the gasin the compression space is pressed back into the intake conduit. Assoon as the closing body of the intake valve completely closes, the gasremaining in the compression space is compressed and pressed into thepressure conduit via the pressure valve. In this way, during backflowregulation, only a part of the maximum-possible gas stream is conveyedfrom the compression space into the pressure conduit via the pressurevalve.

With the backflow regulation method, the fact that the opening time ofthe self-acting pressure valve is reduced proportionately for smallerdelivery quantities is disadvantageous, as is the fact that for deliveryquantities of less than 40% of the rated delivery quantity the openingtime of the pressure valve is reduced to such an extent that the openingand shutting speeds of the pressure valve can increase by multiples. Onthe one hand, this leads to increased wear of the self-acting pressurevalve and, on the other hand, this reduces the range within whichpartial delivery quantities may be reliably conveyed. A furtherdisadvantage of backflow regulation is that the gas is more stronglyheated prior to compression due to the longer dwell time in thecompression space and due to heat transfer via the cylinder wall and dueto a leak stream via the piston. This results in the gas on the pressureside having a raised temperature.

In an advantageous embodiment, the method according to the invention hasthe advantage that, through combined use of back flow regulation andskip regulation, the quantity delivered by the reciprocating compressorcan be varied across a wide range, in particular with no additional wearof the closing body of the intake valve and/or pressure valve. Forregulation of the delivery quantity, there are essentially preferablythree different methods available which may be used. Alongside a methodwith maximal delivery quantity, in which the intake valve shutsautomatically, also the backflow regulation method as already describedand the skip regulation method as already described. For example,regulation dependent on the quantity of fluid to be delivered at anyparticular time may be brought about as follows:

-   -   For delivery of the maximal delivery quantity, no influence is        exerted on the intake valve, which thus opens and closes in a        self-acting manner.    -   For large delivery streams, i.e. delivery quantities in the        range of between about 100% and 80% of the maximal delivery        quantity, continuously variable backflow regulation is deployed.        Although it is also possible that not every cycle of crank        rotation is regulated with backflow regulation, but rather that        the intake valve is operated automatically (i.e. without        exerting influence), for example , for one or two cycles. This        method has the advantage that the unloader is called for less        such that longer service life results and that quantity        regulation itself uses up less energy.    -   For medium-sized delivery streams, i.e. with delivery quantities        in the range of between about 80% and 50% of the maximal        delivery quantity, continuously variable backflow regulation is        used for each cycle.    -   For small delivery streams, i.e. with delivery quantities in the        range of between about 50% and 0% of the maximal delivery        quantity, the closing body of the intake valve is held open        during, for example, one or two cycles, by means of skip        regulation. For the other cycles, the intake valve can either be        operated in a self-acting way or, additionally, if required,        backflow regulation may be deployed.

It is particularly advantageous for the intake valve to be influenced bythe control device and the unloader such that the closing body of thepressure valve of the reciprocating compressor is opened during at leasta predetermined range of opening angle of crank rotation. The range ofopening angle is at least 10° and preferably at least 20° to 30°.

Both of the method according to the invention and the reciprocatingcompressor according to the invention have the advantage that the strokemovement and/or the speed of the unloader is very precisely controllablewith the help of a drive mechanism, preferably an electromagnet, in sucha way that the closure speed of the closing body can be reduced prior toits seating on the intake valve, such that the closing body impinges onthe intake valve at limited speed and comes to rest there such that theclosing body thus seats ‘gently’ on the intake valve, which can bereferred to in English as a ‘soft landing’. In a particularly preferredmethod, the speed of the closing body during seating on the intake valveis less than 0.1 m/s, such that the closing body 5 b has a permittedimpingement speed of less that 0.1 m/s during impingement on the valveseat 5 a of the intake valve 5. This advantageous method reduces wear ofthe closing body considerably and, more advantageously, additionallyresults in operation of the valve having a low noise level.

In a further advantageous embodiment, the drive mechanism comprises acontrollable damping mechanism, in order to influence the speed of theunloader and, in particular, the location of reduced speed, such thatthe closing body impinges on the intake valve with limited speed whenclosing, such that the closing body thus seats ‘gently’ on the intakevalve and shuts it. It is particularly advantageous both that thedamping mechanism be electrically controllable and that it comprises anelectrorheological or magnetorheological fluid, whose viscosity iselectrostatically or electromagnetically variable, such that damping isvery quickly variable via electrical signals. The damping mechanism canhowever also be based on another principal and for example may take theform of an electromagnet.

The invention is described in detail in the following with the help ofembodiment examples.

SHORT DESCRIPTION OF THE DRAWINGS

The drawings used for explanation of the embodiment examples show:

FIG. 1 a longitudinal cross-section through a controllable valve;

FIG. 2 an example of the movement of the unloader, of the closing bodyof the intake valve as well as the speed of the unloader as a functionof crank angle;

FIG. 3 the progression of pressure in the compression space of thereciprocating compressor for differing operating methods;

FIG. 4 the progression of valve travel of the intake valve and of thepressure valve for the operating methods shown in FIG. 3;

FIG. 5 a load progression in a PV-diagram for differing operatingmethods;

FIG. 6 characteristic variables of the valve as a function of crankangle;

FIG. 7 schematically a reciprocating compressor;

FIG. 8 schematically a control device for operation of the gripperacting on the intake valve;

FIG. 9 schematically a further control device for operation of thegripper acting on the intake valve.

In principle, the identical parts are provided with the same referencesigns in the drawings.

WAYS OF CARRYING OUT THE INVENTION

FIG. 1 shows a longitudinal cross-section through a controllable valve 1comprising a compressor housing 4 with an intake valve 5 arrangedtherein, whose position is influenced by an unloader 6, wherein theunloader 6 is actuated by a control device 2, arranged outside of thecompressor housing 4, via a connection means 7, in the form of aconnection rod.

The compressor housing 4 comprises a lamp 4 a, a gas space 4 b, acompression space 4 c and a cover 4 d, wherein the compressor housing 4also comprises a non-depicted or, as the case may be, an unseen pressurevalve 8, via which the compressed fluid may escape from the compressionspace 4 c. The self-acting intake valve 5 comprises a valve seat 5 a, aclosing body 5 b, which is mounted so as to be movable in a strokedirection B and is referred to in the following as valve plate 5 b, avalve backstop 5 c, as well as a return spring 5 d. The unloader 6comprises a plurality of gripper extensions 6 a or fingers 6 a, a guide6 b as wells as a pressure spring 6 c. The unloader 6 is slidablymounted in stroke direction B, driven by the electromagnet 2 a, whereinthe tip of the gripper extensions 6 a can lie against the valve plate 5b, depending on the stroke in direction B, and in particular, can pushthe valve plate 5 b against the valve backstop 5 c, such that the valveplate 5 b is no longer movable, and the valve 5 thereby stays open byforce. The control device 2 comprises an electromagnet 2 a, as a drivingmechanism, with a magnet anchor 2 b, a magnet core 2 c as well as amagnet coil 2 d. The control device 2 further comprises a housing 2 m,which is connected with the compressor housing 4 via a connection part 2e. The control device also comprises a steering mechanism 2 i or aregulating mechanism 2 i, electrical conductors 2 k, 2 l, wherein theelectrical conductor 2 l connects the steering mechanism 2 i with theelectromagnet 2 a. The control device 2 comprises two guides 2 f, 2 g tomount the electromagnet 2 a and the connection rod 7 slidably in strokedirection B. A filter 3 can also be provided. In an advantageousembodiment, the control device 2 also comprises a displacement sensor 2h, which captures the stroke or, respectively, the position of theelectromagnet 2 a or, respectively, the position of the unloader 6 instroke direction B.

The controllable valve 1 shown in FIG. 1 can now be steered via thecycles of crank rotation in different ways. A cycle is to be understoodas a 360° rotation of the reciprocating compressor crankshaft.

FIG. 2 shows the operation of a continuously variable backflowregulation, wherein what is shown in FIG. 2 are the stroke movement A ofthe unloader 6, the stroke movement B of the valve plate 5 b and thespeed C of the unloader 6 as functions of the crank angle, wherein asingle rotation of the crankshaft is depicted, i.e. FIG. 2 shows angularprogression from 0° to 360°. It can be seen from the valve plate's 5 bstroke movement B, that the valve plate 5 b automatically opens duringthe intake, in the angular range of about 90° to 110° in the embodimentexample shown, such that the valve plate 5 b lies against the valvebackstop 5 c. In the operation of the continuously variable backflowregulation, after opening of the valve plate 5 b, the unloader 6 ismoved or, respectively, made to travel, as depicted by way of example bycurve A, until it lies against the valve plate 5 b. The speed of theunloader 6 is also shown in FIG. 2 by curve C. When operating inself-acting mode, the intake valve 5 would automatically shut when thepiston changes direction—at 225° in the example shown. Thus, theoperation of a continuously variable backflow regulation has the effect,that the unloader 6 lies against the closing body 5 b, during a firstsection K1 of the cycle of crank rotation, and prevents its shutting,and that the unloader 6 is driven back according to the progression ofcurve A2, during a second section K2 of the cycle of crank rotation,wherein, due to the prevailing pressure conditions, the closing body 5b, namely the valve plate 5 b, follows the movement of the unloader 6or, respectively, lies against the unloader 6, such that the valve plate5 b lies on the valve seat 5 a at some point in time—at about 290° inthe example shown—and shuts the valve 5. In the further section K3, theunloader 6 is made to travel still further, so that it, for example, isdistanced from the valve plate 5 b.

The movement of the closing body 5 b is influenced in section K2 by thedrive mechanism, in the embodiment example shown by the electromagnet 2a and the connection rod 7, in such a way that the unloader 6 has, as afunction of crank rotation, the progression of travel A shown in FIG. 2or, respectively, the progression of speed C shown in FIG. 2, whereinthe electromagnet 2 a is steered in such a way that the speed of themoving closing body 5 a is reduced prior to seating on the intake valve5, as is shown in FIG. 2. In a particularly advantageous embodiment, theunloader 6 is even thereafter made to travel into an end position in afurther section K3, advantageously as shown in curve C by the “secondhump”, in which another acceleration followed by another braking occurs,such that the unloader 6 comes to rest, as shown by progression oftravel A at section K3, at a distance from, i.e. without direct contactwith, the closing body 5 a. In an advantageous method step, theelectromagnet 2 a is steered such that the closing body 5 b has a speedof less than 0.1 m/s while seating on the intake valve.

The valve 1 can also be operated by skip regulation methods. With skipregulation, the unloader 6 is made to travel in such a way that itprevents shutting of the closing body 5 b for the duration of a wholecycle of crank rotation, advantageously in such a way that the unloader6 lies against the closing body 5 b during the whole cycle, such thatthe latter remains opened over the whole cycle.

FIG. 7 shows schematically a reciprocating compressor comprising acompressor housing 4 with a movably mounted piston 4 e, which, in part,delimits a compression space 4 c, and which is driven by a piston rod 4f. On the compressor housing 4, there is also an intake valve 5, viawhich the fluid or gas, which is to be conveyed, is aspirated. Thereciprocating compressor also comprises a gripper 6, which is driven bya control device 2 comprising a drive mechanism. The control device 2,the intake valve 5 and the gripper 6 form a controllable valve 1. On thecompressor housing 4, there is also a pressure valve 8, via which thecompressed gas leaves the compression space 4 c. The reciprocatingcompressor can, of course, also comprise a plurality of compressionspaces 4 c, wherein each compression space 4 c comprises a separatepiston 4 e with piston rod 4 f, and wherein each compression space 4 ccomprises a separate, controllable valve 1.

FIG. 3 shows now the progression of pressure in a compression space 4 cof a reciprocating compressor as a function of crank angle for differingoperating methods. In the embodiment example shown, bottom dead centre,U_(TP), lies at 90°, i.e. at this position the compression space 4 creaches maximum volume. Top dead centre, O_(TP), lies, in this example,at 270°, i.e. at this position the compression space 4 c reaches minimumvolume. In the first section D, the movement of the closing body 5 b ofthe intake valve 5 occurs automatically, resulting in the shownprogression of pressure over a 360° crank angle. Movement of the closingbody of the pressure valve 8 always occurs automatically in FIG. 3. Inthe embodiment example shown, the pressure on the pressure side is, forexample, about 3.1 bar, wherein the pressure valve 8, in the embodimentexample shown including valve spring biasing, opens itself at a pressureof about 3.2 bar. The pressure valve 8 opens at, say, a crank angle of190°. The self-acting pressure valve 8 is completely opened, in thedepicted embodiment example, during an angular range K_(w) of about 50°because the pressure valve 8 has maximal valve travel in thismaximally-open-angular-range K_(w), before the pressure valve 8 closesagain. The total opening angle K_(v), during which the valve is open,i.e. the closing body is lifted from the valve seat, or, respectively,the total opening time of the pressure valve 8 is appx. 80°. In thesecond section E, a skip regulation is depicted, during which, aspreviously described, the closing body 5 b is held open over the wholecrank angle of 360°, resulting in the shown progression of pressure inthe compression space 4 c. The pressure in the compression space 4 cremains at all times below 3.2 bar, such that the pressure valve 8 doesnot automatically open. In the third section F, a continuously variablebackflow regulation is depicted, during which, as described in FIG. 2,the closing body 5 b is held open by the unloader during a part of thecrank angle of 360°, such that the accumulation of pressure in thecompression space 4 c occurs later in relation to crank angle, resultingin the shown progression of pressure. The pressure valve opens at, say,a crank angle of 210°. The self-acting pressure valve 8 remainscompletely opened in the depicted embodiment example during amaximally-open-angular-range K_(w) of about 30° before the valve travelreduces, as shown in FIG. 4, and the valve 8 completely closes againafter the total opening angle K_(v). The total opening angle K_(v),during which the valve is opened, or, respectively, the total openingtime of the valve is appx. 60°.

With skip regulation, the intake valve 5 is thus held open during acomplete working stroke. In this way, the aspirated gas is pressed backinto the intake conduit during the compression phase and thus is notavailable for compression and further transport in the pressure conduit.The compression space does not convey any gas. If skip regulation isdeactivated, the compression space once again conveys the full fluidstream.

By contrast, with constantly variable backflow regulation, the closingbody 5 b of the intake valve 5 is only pressed open for the beginning ofthe compression phase. In this way, a part of the gas is pressed backinto the intake conduit. If the intake valve 5 shuts, then the gasremaining in the compression space can be compressed and pressed throughthe pressure valve into the pressure conduit. The compression space onlyconveys a part of the maximum-possible gas stream.

Both methods use the unloader 6 to press the sealing element 5 b of thevalve 5, for example a plate, ring or poppet valve, against the valvebackstop 5 c and thus into the open position. Since for constantlyvariable backflow regulation, in one working cycle, the unloader 6 hasto be moved from the closed to the open position and back again, andsince for skip regulation a longer time is available for the samesequence of movements, the power uptake, the required forces, thetravelling speeds and the stress-requirements of the parts used arehigher for constantly variable backflow regulation.

As indicated in FIG. 3, the delivery quantity of a reciprocatingcompressor can now be regulated over a wide range by a combination ofconstantly variable backflow regulation F and skip regulation E,wherein, beyond this, section D can also be used for delivery quantityregulation, during which the closing body moves automatically. Thesethree types of actuation D, E, F of the operation of valve 5 can now becombined together in any desired manner, such that, for example,initially during successive cycles only actuation type D, E or F occursand later on, for example, a combination of at least two of the threeactuation types D, E and F.

For example, the valve could be steered in such a way that variousdelivery quantities are regulated in such a way, that, for largedelivery streams, the intake valve 5 is automatically driven duringcertain cycles and is driven with constantly variable backflowregulation during certain cycles; that, for middle-sized deliveryquantities, the intake valve 5 is driven during every cycle withconstantly variable backflow regulation; and that, for small deliveryquantities, the intake valve 5 is constantly held open during certaincycles, and driven with constantly variable backflow regulation duringcertain cycles.

FIG. 4 shows the stroke movement 8 c of the pressure valve 8 as afunction of crankshaft angle. The stroke movement 5 e of the closingbody 5 b of the intake valve 5 is also shown as a function of crankshaftangle. Movement of the pressure valve 8 occurs automatically, whereas,as previously described, movement of the closing body 5 b of the intakevalve 5 is determined by the gripper 6 with skip regulation E andbackflow regulation F. In FIG. 4, the maximally-open-angular-range K_(w)is well-recognisable, within which the valve 8 has a maximal valvestroke, i.e. is maximally opened. Also visible is the total openingangle K_(v), during which the valve 8 is opened.

The duration of opening of the self-acting pressure valve 8 isdetermined by the angular range, during which the pressure in thecompression space 4 c lies above the opening pressure of the pressurevalve 8; in the embodiment example of FIG. 3 above a pressure of 3.2bar. From the constantly variable backflow regulation shown by F inFIGS. 3 and 4 it may be seen that the later the closing body 5 b isshut, the more the angular range of opened pressure valve 8 reducesitself. Especially with small delivery quantities, this has the resultthat, if backflow regulation were constantly used then the pressurevalve 8 would only be opened during a very short total opening angleK_(v). In order to raise the total opening angle K_(v) of the pressurevalve 8 with small delivery quantities, the reciprocating compressor isrun in such a way that skip regulation E is used during one or severalcrank cycles, in order to convey a sufficiently large quantity of gas inthe succeeding backflow regulation F, such that the pressure valve 8remains opened over a total opening angle K_(v) of at least 10° andpreferably over a total opening angle K_(v) of at least between 20° and30°. This results in the pressure valve 8 being opened long enough toavoid excessive strikes or excessive opening and shutting speeds. Thisextends the operating life of the pressure valve considerably. FIG. 5shows a load progression in a PV-diagram under different operatingmethods, namely as already shown in FIG. 3, at full load D withself-acting intake valve 5, with skip regulation E and with constantlyvariable backflow regulation F.

A compressor can be arranged such that, as shown in FIG. 7, it has onlyone compression space 4 c per cylinder, wherein, in the following, sucha compression space is also referred to as upper compression space. Acompressor can also be arranged such that it has a second compressionspace in the same cylinder, which is separated from the firstcompression space by the piston 4 e, such that during movement of thepiston 4 e, the fluid in one compression space is compressed and in theother compression space is aspirated. In the following, the secondcompression space is also referred to as lower compression space. In aparticularly advantageous method, delivery quantity regulation occurs asindicated in FIG. 3 such that the pressure valve 8 of the reciprocatingcompressor opens at least during a predetermined angular range Δ of 20°to 30° before reaching top dead centre O_(TP) (for the upper compressionspace) respectively bottom dead centre U_(TP) (for the lower compressionspace, in the case of the cylinder comprising two compression spaces) ofthe crank rotation. The advantage of this method is that only the timingof opening needs to be determined, since the timing of shutting is knownto some degree and for an idealised valve, lies at dead centre of theupper or, respectively, if present, lower compression space.

The opening time of the pressure valve 8 can, for example, be determinedby measuring the pressure in the compression space and comparing thiswith the final pressure, or given knowledge of the operationalconditions of the compressor, by a previous, respectively simultaneouscalculation of the maximal opening time of the intake valve around thereversal point of piston movement, so that the pressure valve's minimalopening time is not fallen below.

FIG. 6 show characteristic variables of the controllable valve 1 as afunction of crank angle, respectively, angle of rotation, for obtainingthe progression of movement B of the valve plate 5 b and the progressionof movement A of the unloader 6 as shown in the path diagram in FIG. 6.The progression of the speed of the unloader 6 is also shown in curve C.Also, the force G applied by the electromagnet 2 a is shown in curve Gand the required current H for steering of the electromagnet 2 a isshown. The progressions shown in FIG. 6 are, in particular, important inbringing about the ‘gentle landing’ of the valve plate 5 b on the valvebackstop 5 c set out in FIG. 2.

FIG. 8 shows schematically a further embodiment example of a controldevice 2 for actuating and driving the gripper 6 acting on the intakevalve 5. The control device 2 comprises a drive mechanism 2 n, which isconnected with the gripper shown schematically in FIG. 7 via theconnection rod 7, which is mounted so as to be linearly movable. Thedrive mechanism 2 n shown in this embodiment example comprises a lineardrive 2 w as well as a steerable damping mechanism 2 o, wherein thedamping mechanism 2 o has the task of damping motion produced by thelinear drive 2 w in an electrically steerable way such that the gripper6 respectively the valve plate 5 b of the intake valve 5 moves as, forexample, shown in FIG. 2. The linear drive 2 w has a linearly movableconnection rod 2 t, which is functionally connected with the connectionrod 7. In the embodiment example shown, the damping mechanism 2 o isarranged between the linear drive 2 w and the gripper 6. The dampingmechanism 2 o could however also be arranged at another position, forexample, in the depicted view of the control device 2, also above thelinear drive 2 w. The damping mechanism 2 o can take many differentpossible forms to be able to effect a damping of the motion of thelinear drive 2 w. The damping mechanism 2 o shown schematically in FIG.8 is particularly advantageous for bringing about the ‘gentle landing’of the valve plate 5 b on the valve backstop 5 c as per the invention.The damping mechanism 2 o comprises a cylinder 2 p and internal to thisa linearly slidable piston 2 r, which divides the internal space of thecylinder 2 p into a first internal space 2 q and a second internal space2 s. The two internal spaces 2 q, 2 s are connected to each other via afluid-conducting connection 2 u, such that a fluid is exchangeablebetween the two internal spaces 2 q, 2 s. In an advantageous embodiment,the two internal spaces 2 q, 2 s are fluid-conductively connected witheach other via an electrically steerable damping or choke 2 v. Asteering and regulating device 2 i is signal-conductively connected withboth the linear drive 2 w and the steerable damping 2 v via electricalconductors 2 k, 2 l, such that both the linear drive 2 w and the dampingproperties of the damping mechanism 2 o are steerable, in order to steerthe position or, respectively, the speed of the valve plate 5 b in sucha way that a ‘gentle landing’ of the valve plate 5 b is achieved, asshown by way of example in FIG. 2.

The fluid conductive connection 2 u as well as the electricallysteerable damping 2 v could also be arranged on the damping mechanism 2o of inside the damping mechanism 2 o, in particular, also at the piston2 r, by providing the piston 2 r, for example, with a fluid-conductiveconnection between the first and second internal space 2 q, 2 s.

In a particularly advantageous embodiment, the fluid of the dampingmechanism 2 o consists at least partially of an electrorheological ormagnetorheological liquid. Such liquids have the property that theirviscosity is electrically steerable, such that with such liquids, anelectrically-controllable choking section can be brought about. Such achoking section has the advantage that the viscosity can be varied overa wide range and that the viscosity can be varied very quickly with thehelp of an electrical signal. The damping properties of such a dampingmechanism 2 o are thereby very rapidly variable, such that the movementof the piston 2 r and therewith the movement of the connection rod 7, ofthe gripper 6 and ultimately of the valve plate 5 b can be damped or,rather, can be steerable and regulatable, in such a way that the valveplate 5 b carries out a ‘gentle landing’ with respect to distancetravelled and speed.

Damping mechanisms comprising an electrorheological ormagnetorheological liquid are, for example know from the document WO2008/141787A1 or from the document EP 1 034 383 B1.

The linear drive 2 w can take the form of, for example, an hydraulic orpneumatic drive, an electromagnetic drive, a linear motor or anelectrical motor with a transmission.

FIG. 9 shows a further embodiment example of a control device 2. Incontrast with the embodiment shown in FIG. 8, the damping mechanism 2 oin FIG. 9 comprises an electrically controllable three-way valve 2 y, anon-variable choke 2 x as well as fluid conduits 2 u ₁ and 2 u ₂. Thedamping properties of the damping mechanism 2 o are controllable via theelectric three-way valve 2 y, through the latter allowing the fluidwhich is exchanged between the first and second internal space 2 q, 2 sflow either via fluid conduit 2 u ₁ or fluid conduit 2 u ₂ and the choke2 x. The damping mechanism 2 o could also comprise a plurality of chokes2 x with various choking effects, as well as a multi-port valve, whichcan controllably and selectively guide the fluid to each of thesechokes, such that the damping mechanism 2 o has a plurality of differentdampings.

In a further advantageous embodiment, the damping mechanism 2 o could bearranged such that the braking energy that is given up by the dampingmechanism 2 o to the closing body 5 b can be recovered. For example, thedamping mechanism 2 o could be an eddy current brake. The dampingproperties of such an eddy current brake could also be electricallycontrollable. In a particularly advantageous embodiment, the dampingmechanism 20 thus takes the form of a controllable eddy current brake,which, on the one hand, allows a steering of the damping properties andwhich, on the other hand, allows energy recovery, wherein for energyrecovery, electrical energy is produced by preference. Since theunloader 6 is operated very quickly and very often during backflowregulation, a damping mechanism 2 o with energy recovery is particularlyadvantageous for reducing the overall energy demand for intake valve 5operation or, respectively, for operation of the unloader 6. Alsowarming, which occurs during operation, is advantageously reduced.

1. Method for delivery quantity control of a reciprocating compressor,in which the movement of a closing body (5 b) of a self-acting intakevalve (5) is influenced during at least part of a cycle of crankrotation by an unloader (6) driven by a control device (2), wherein themethod comprises a continuously variable backflow regulation, in whichthe unloader (6) lies against the closing body (5 b) during a firstsection (K1) of the cycle of crank rotation and prevents its closure,and in which the unloader (6) is driven back during a second section(K2) of the cycle of crank rotation and the closing body (5 b) isclosed, wherein the unloader (6) is driven back in such a way that thespeed of the moving closing body (5 b) is reduced prior to its seatingon the intake valve (5).
 2. Method for delivery quantity regulationaccording to claim 1, characterised in that the method comprises a skipregulation, in which the unloader (6) prevents closure of the closingbody (5 b) during a whole cycle of crank rotation, wherein the deliveryquantity is regulated by at least a combination of continuously variablebackflow regulation and skip regulation.
 3. Method according to claim 1,characterised in that, during seating on the intake valve (5), the speedof the closing body (5 b) falls below a permitted impingement speed, andthat this is less than 0.1 m/s.
 4. Method according to claim 1,characterised in that, after the seating of the closing body (5 b), thecontrol device (2) moves the unloader (6) still further and then bringsit to rest, in order to distance the unloader (6) from the closing body(5 b) and to bring the unloader (6) to an end position.
 5. Methodaccording to claim 1, characterised in that, after the seating of theclosing body (5 b), during a third section (k3) of the crank rotation,the control device (2) once again accelerates the unloader (6) and thenbrings it to rest, in order to distance the unloader (6) from theclosing body (5 b) and to bring the unloader (6) to an end position. 6.Method according to claim 1, characterised in that, the control device(2) comprises an adaptive pre-control with which the stroke (A) and thespeed (C) of the unloader (6) are regulated.
 7. Method according toclaim 1, characterised in that, the intake valve (5) is influenced bythe control device (2) and the unloader (6) in such a way that a closingbody (8 b) of a pressure valve (8) of the reciprocating compressor isopened during at least a predetermined total opening angle (K_(v)) of acrank rotation.
 8. Method according to claim 7, characterised in that,the predetermined total opening angle (K_(v)) is at least 10°, andpreferably lies at least in the range between 20° and 30°.
 9. Methodaccording to claim 1, characterised in that, the intake valve (5) isinfluenced by the control device (2) and the unloader (6) in such a waythat a closing body (8 b) of a pressure valve (8) of the reciprocatingcompressor is opened at least during a predetermined angular range (Δ)of a crank rotation before the upper, respectively lower dead centre(O_(TP), U_(TP)).
 10. Method according to claim 9, characterised inthat, the predetermined angular range (Δ) is at least 10°, andpreferably lies at least in the range between 20° and 30°.
 11. Methodaccording to claim 1, characterised in that, various delivery quantitiesare regulated in such a way, that, for large delivery streams, theintake valve (5) is automatically driven during certain cycles and isdriven with constantly variable backflow regulation during certaincycles; that, that, for middle-sized delivery quantities, the intakevalve (5) is driven during every cycle with constantly variable backflowregulation; and that, for small delivery quantities, the intake valve(5) is constantly held open during certain cycles under skip regulation,and driven with constantly variable backflow regulation during certaincycles.
 12. Reciprocating compressor with delivery quantity regulation,in particular with constantly variable delivery quantity regulation,with an unloader (6) arranged on at least one self-acting intake valve(5) of the compressor, with a control device (2) for driving theunloader (6), as well as with a closing body (5 b) of the intake valve(5), wherein the unloader (6) acts on the closing body (5 b) in such away that the intake valve (5) is opened over a controllable part of theworking stroke of the compressor, characterised in that, the controldevice (2) comprises a drive mechanism (2 n) which acts via a connectionmeans (7) on the unloader (6), wherein the control device (2) comprisesa constantly variable backflow regulation, in which the unloader (6)lies against the closing body (5 b) during a first section (K1) of thecycle of crank rotation and prevents its shutting, and in which theunloader (6) returns during a second section (K2) of the cycle of crankrotation such that the closing body (5 b) shuts, and wherein the controldevice (2) preferably comprises a skip regulation, in which the unloader(6) prevents the shutting of the closing body (5 b) during a completecycle of crank rotation, and wherein the control device (2) isconfigured to steer drive mechanism (2 n) and thereby the unloader (6)in such a way that the speed of the closing body (5 b) is reduced priorto its seating on the intake valve (5), in order to seat the closingbody (5 b) gently on the intake valve (5).
 13. Compressor according toclaim 12, characterised in that, the control device (2) comprises amechanism for measuring and/or calculating the pressure progression (P)in the compression space of the reciprocating compressor, and that thecontrol device (2) is configured such that it drives the closing body (5b) via the unloader (6) in free-running mode or with backflow regulationor with skip regulation, in order to open the pressure valve (8)automatically during a total opening angle (K_(v)).
 14. Compressoraccording to claim 12, characterised in that, the control device (2)comprises a displacement sensor (2 h), which captures the displacementof the drive mechanism (2 n) and/or of the unloader (6) and/or of theclosing body (5 b).
 15. Compressor according to claim 12, characterisedin that, the drive mechanism (2 n) is in the form of an electromagnet (2a) with solenoid, with a movable magnet anchor (2 b) and a fixedlyarranged magnet core (2 c) with magnet coil (2 d), wherein theconnection means (7) is fixedly connected with the magnet anchor (2 b),and wherein the magnet anchor (2 b) is mounted so as to be movable inthe direction of extension of the connection rod (7).
 16. Compressoraccording to claim 12, characterised in that, the drive mechanism (2 n)comprises a steerable damping mechanism (2 o), for damping the speed ofthe unloader (6).
 17. Compressor according to claim 16, characterised inthat the damping mechanism (2 o) is electrically steerable, and that thedamping mechanism (2 o) comprises an electrorheological ormagnetorheological liquid.